title: ErbB2 upregulates the Na+,HCO3(-)-cotransporter NBCn1/SLC4A7 in human breast cancer cells via Akt, ERK, Src, and Kruppel-like factor 4.
abstract: Misregulation of acid-base transport plays central roles in cancer development. We previously demonstrated the strong up-regulation of the Na(+),HCO3(-) cotransporter NBCn1 (SLC4A7) in MCF-7 breast cancer cells by a truncated, constitutively active ErbB2 (HER2) receptor, ΔNErbB2, and showed that NBCn1 expression and activity are increased in breast cancer tissue from patients. Here, we present the first in-depth characterization of an SLC4A7 promoter and identify its minimal ΔNErbB2-sensitive region. Inhibition or siRNA-mediated knockdown of PI3K, Akt1, ERK1/2, or Src decreased the NBCn1 protein level in ΔNErbB2-expressing MCF-7 cells by ~50, 60, 30 and 35%, respectively. Further, knockdown of the transcription factor Krüppel-like factor 4 (KLF4) reduced NBCn1 protein expression by ~40%, and KLF4 overexpression increased NBCn1 expression by 50-80%. In contrast, knockdown of the closely related transcription factor specificity protein 1 (Sp1) or transfection with dominant-negative Sp1 increased NBCn1 expression by ~35 and ~50%, respectively. NBCn1 expression was also increased by stimulation of full-length ErbB1, -2, and -3 receptors in SKBr3 cells (1.5- and 2-fold by NRG1 or EGF, respectively) or after their exogenous expression in MCF-7 cells. Finally, stimulation with NRG1 or EGF more than doubled acid extrusion capacity in SKBr3 cells. In conclusion, NBCn1 is strongly upregulated by ErbB receptor signaling in a manner involving opposite effects of KLF4 and Sp1, transcription factors with central roles in cancer development. ErbB-induced up-regulation of NBCn1-mediated acid extrusion may play important physiological and pathophysiological roles in the breast epithelium and other tissues with high ErbB receptor levels.
authors.affiliation: 1Department of Biology, University of Copenhagen, 13, Universitetsparken, DK-2100 Copenhagen, Denmark. sfpedersen@bio.ku.dk.
authors.forename: Andrej
authors.initials: A
authors.lastname: Gorbatenko
authors.forename: Christina W
authors.initials: CW
authors.lastname: Olesen
authors.forename: Nina
authors.initials: N
authors.lastname: Mørup
authors.forename: Gerald
authors.initials: G
authors.lastname: Thiel
authors.forename: Tuula
authors.initials: T
authors.lastname: Kallunki
authors.forename: Eivind
authors.initials: E
authors.lastname: Valen
authors.forename: Stine F
authors.initials: SF
authors.lastname: Pedersen
mesh_terms: D045744:Cell Line, Tumor; D048049:Extracellular Signal-Regulated MAP Kinases / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D027982:Sodium-Bicarbonate Symporters / Q000235:genetics / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*; D019061:src-Family Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D048049:Extracellular Signal-Regulated MAP Kinases; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors; D051057:Proto-Oncogene Proteins c-akt; D018719:Erb-b2 Receptor Tyrosine Kinases; D027982:Sodium-Bicarbonate Symporters; D017923:Sodium-Hydrogen Exchangers; D019061:src-Family Kinases; C000715467:KLF4 protein, human; C422022:SLC4A7 protein, human
keywords: HER2; KLF4; MCF-7